United States Department of Transportation
i
Evaluating roadway subsurface drainage practices - phase II.
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2015-04-01
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[PDF-6.77 MB]
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Abstract:Well-performing subsurface drainage systems form an important aspect of pavement design by the Iowa Department of
Transportation (DOT). The recently completed Iowa Highway Research Board (IHRB) project TR-643 provided extensive
insights into Iowa subsurface drainage practices and pavement subdrain outlet performance. However, the project TR-643 (Phase
I) forensic testing and evaluation were carried out in a drought year and during the fall season in 2012. Based on the findings of
IHRB Project TR-643, the Iowa DOT requested an expanded Phase II study to address several additional research needs: evaluate
the seasonal variation effects (dry fall 2012 versus wet spring/summer 2013, etc.) on subdrain outlet condition and performance;
investigate the characteristics of tufa formation in Iowa subdrain outlets; investigate the condition of composite pavement
subdrain outlets; examine the effect of resurfacing/widening/rehabilitation on subdrain outlets (e.g., the effects of patching on
subdrain outlet performance); and identify a suitable drain outlet protection mechanism (like a headwall) and design for Iowa
subdrain outlets based on a review of practices adopted by nearby states.
A detailed forensic test plan was developed and executed for inspecting the Iowa pavement subdrains in pursuit of fulfilling the
Phase II study objectives. The observed outlets with blockage and the associated surface distresses in newly constructed jointed
plain concrete pavements (JPCPs) were slightly higher during summer 2013 compared to fall 2012. However, these differences
are not significant. Less tufa formation due to the recycled portland cement concrete (RPCC) base was observed with (a) the use
of plastic outlet pipe without the gate screen–type rodent guard and (b) the use of blended RPCC and virgin aggregate materials.
In hot-mix asphalt (HMA) over JPCP, moisture-related distress types (e.g., reflection cracking) were observed more near blocked
drainage outlet locations than near “no blockage” outlet locations. This finding indicates that compromised drainage outlet
performance could accelerate the development of moisture-related distresses in Iowa composite pavement systems.
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